Simultaneous Removal of Cu2+/Cd2+ by Sulfidized nZVI/MXene Composites: Experimental and DFT Studies

Abstract

The copresence of copper (Cu²⁺) and cadmium (Cd²⁺) in water poses a serious threat to aquatic ecosystems due to their combined toxicity, persistence, and potential for bioaccumulation. Because of the hazardous effects of both ions, the simultaneous removal of Cu²⁺ and Cd²⁺ in aquatic environments is of great significance. Herein, novel sulfide-modified nanozerovalent iron (S-nZVI)/MXene composites were prepared by in situ embedding S-nZVI nanoparticles into an MXene lamellar structure. Different characteristic techniques such as SEM, HRTEM, XRD, FTIR, XPS, and BET suggest that S-nZVI was evenly anchored to the MXene layers, effectively mitigating their clustering. Nitrogen adsorption-desorption showed that the specific surface area of S-nZVI@MXene was approximately 29.77 m²/g, which is 1.64 times more than that of MXene (17.84 m²/g). Batch experiments demonstrated that S-nZVI@MXene exhibits excellent removal efficiency for Cu²⁺ and Cd²⁺ in a binary solution. At pH = 5.4, the maximum adsorption capacities of S-nZVI@MXene for Cu²⁺ and Cd²⁺ were 67.85 and 56.33 mg/g, respectively. The pseudo-second-order kinetic model and Langmuir isotherm model were more suitable for describing the adsorption, implying the nature of single-layer chemical adsorption. Results of experimental and density functional theory (DFT) calculations jointly indicated ion-exchange reactions and surface complication. After three reuses, S-nZVI@MXene maintained removal efficiencies of 97.8% and 62.54% for Cu²⁺ and Cd²⁺, respectively. S-nZVI@MXene shows great potential as an adsorbent for simultaneously removing Cu²⁺ and Cd²⁺ from wastewater.